1. Field of the Invention
The present invention relates to a band distribution inspecting device and band distribution inspecting method for measuring a frequency distribution in a scattered oscillation signal oscillated containing a frequency variation from the fundamental frequency and particularly, to a band distribution inspecting device and band distribution inspecting method for determining a band distribution in the frequency variation in a short time.
2. Description of Related Art
In recent years, electronic apparatuses such as personals computer and printers have become highly functional so that high-speed operation and high-density integration have been progressed. Thus, in addition to employing higher frequency as the oscillation frequency of a clock signal supplied to electronic apparatuses and increased emission of electromagnetic interference (hereinafter referred to as EMI) in oscillation frequency and harmonics, influences upon adjoining components and devices of the EMI cannot be neglected.
As a countermeasure for reducing the EMI intensity, recently, spectrum scattering technology has attracted public attention. If the spectrum scattering technology is applied to the oscillation frequency of the clock signal, the oscillation frequency of the clock signal can be changed cyclically from the fundamental frequency. As a result, the EMIs emitted from the spectrum-scattered clock signal or/and an electronic apparatus driven by the scattered clock signal are scattered for each frequency. The EMI intensity is never increased by a specific frequency and the EMI intensity of harmonic component can be reduced.
Here, the EMI intensity peak decreases depending on the frequency band scattered by the frequency variation from the fundamental frequency. As the scattering rate increases, the EMI intensity peak decreases. The reason is that if a wider frequency scattering occurs, the EMI intensity emitted at each frequency decreases. If the band distribution by the spectrum scattering is adjusted depending on usage environment of an electronic apparatus or permissible EMI intensity, the EMI intensity can be reduced within an oscillation frequency permitted to the clock signal from the viewpoint of the operation specification of electronic apparatus.
For a device and apparatus on which the spectrum scattering technology is applied, it is necessary to inspect that the band distribution can be adjusted depending on the setting. This is outgoing inspection for a device or apparatus. Band distribution of the oscillation frequency upon the scattered clock signal is carried out according to measurement by a spectrum analyzer or analysis or the like on data acquired by a digitizer.
Measurement by the spectrum analyzer or digitizer can acquire the occupation rate of each frequency component accurately which the spectrum-scattered clock signals occupy in an entire range of the measurement frequency.